Kepler multiplanet systems analysis (Q1-Q8)

In addition, many Kepler multiplanet systems have planets with orbital periods less than a few days. With the exception of Kepler-42, however, there are no examples of systems with both short orbital periods and nearby companion planets while our statistical analysis predicts ~17 such pairs.

For orbital periods of the inner planet that are less than three days, the minimum period ratio of adjacent planet pairs follows the rough constraint P=P_2_/P_1_>~2.3(P_1_/day)^-2/3^ (equation (1)). This absence is not due to a lack of planets with short orbital periods. We also show a statistically significant excess of small, single-candidate systems with orbital periods below three days over the number of multiple candidate systems with similar periods--perhaps a small-planet counterpart to the hot Jupiters.